The present invention relates to a novel working fluid for traction drive or, more particularly, to a working fluid for traction drive having a high traction coefficient at high temperatures.
A working fluid for traction drive as usually meant is an oily fluid used in various kinds of traction drive apparatuses, i.e. friction drive apparatuses utilizing rolling contact, such as continuously variable transmission for automobiles and industrial machines, hydraulic instruments and the like. Working fluids for traction drive should satisfy several requirements including a high traction coefficient and stability against heat and oxidation as well as inexpensiveness as a matter of course.
As a trend in recent years, studies in the machinery are directed to a design of smaller and smaller or lighter and lighter traction drive apparatuses with automobiles as a main object of the application thereof. Such a smaller and lighter traction drive apparatus is necessarily operated under operating conditions of increasingly high velocity and high load so that a working fluid for traction drive use also should have greatly improved performance accordingly and development of such an improved working fluid is eagerly desired.
Various compounds have hitherto been proposed as useful for the service as a working fluid for traction drive use including, for example, those disclosed in Japanese Patent Publication Nos. 46-338, 36-339, 47-35763, 48-42067, 48-42068 and 53-36105 and Japanese Patent Kokai No. 55-43108 and 55-40726. These compounds, however, are not free from the problem that the traction coefficient thereof is greatly decreased at a high temperature of, for example, 100.degree. to 160.degree. C.
Several compounds are known to have a high traction coefficient at high temperatures including those proposed in Japanese Patent Publication Nos. 60-1353, 60-1354 and 60-43392 and Japanese Patent Kokai No. 60-35095. These compounds, however, are still not quite satisfactory when the traction drive apparatus is to be operated under severer operating conditions or at still higher temperatures. Therefore, it is an important technical problem to develop a working fluid for traction drive use capable of exhibiting greatly improved performance at high temperatures.